Silicon carbide polishing method utilizing water-soluble oxidizers

ABSTRACT

The inventive method comprises chemically-mechanically polishing a substrate comprising at least one layer of silicon carbide with a polishing composition comprising a liquid carrier, an abrasive, and an oxidizing agent.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is a continuation-in-part of copending U.S.patent application Ser. No. 11/515,546, filed Sep. 5, 2006.

BACKGROUND OF THE INVENTION

Semiconductors with the ability to operate more efficiently in order toachieve a significant reduction in power consumption are highlydesirable. Typically, silicon substrates are used in the manufacture ofsuch devices, however, further development is limited due to theinherent characteristics of silicon. Development of the next generationof semiconductor devices has emphasized the use of materials having agreater hardness and other unique properties. For example, siliconcarbide, when compared with silicon oxide, has a higher thermalconductivity, a greater tolerance for radiation, a higher dielectricstrength, and is able to withstand greater temperatures, which makes itsuitable for a variety of applications. The use of silicon carbide hasbeen limited, however, by semiconductor fabrication technology.

In order to produce silicon carbide semiconductors, the surfaces of thesilicon carbide substrates must be polished in order to provide smoothsurfaces and to obtain precise dimensions for the surfaces. Theproperties which make silicon carbide such a useful substrate provideunique challenges in the polishing process. Due to the hardness ofsilicon carbide, diamond grit is typically used to mechanically polishsilicon carbide substrates.

Chemical-mechanical polishing (CMP) techniques are widely usedthroughout the semiconductor industry in order to polish the currentgeneration of silicon devices. CMP involves the use of a polishingcomposition (also known as a polishing slurry) containing an abrasiveand an aqueous material, which is applied to a surface by contacting thesurface with a polishing pad saturated with the polishing composition.The polishing composition may also contain an oxidizing agent, whichallows for less aggressive mechanical abrasion of the substrate, thusreducing mechanical damage to the substrate caused by the abradingprocess. The use of such techniques to polish silicon carbide substratescould greatly reduce the costs of manufacturing semiconductors bydecreasing polish time and reducing damage to the substrate.

Adaptation of CMP techniques for silicon carbide polishing has beenrelatively unsuccessful. Polishing compositions containing colloidalsilica resulted in low silicon carbide removal rates, thus requiring alengthy polishing cycle lasting several hours at temperatures of around50° C., which is likely to result in damage to the silicon carbidesubstrate. Zhou, et al., J. Electrochemical Soc., 144, p. L161-L163(1997); Neslen, et al., J. Electronic Materials, 30, p. 1271-1275(2001). The long polishing cycle adds considerable cost to the processand is a barrier preventing widespread use of silicon carbide within thesemiconductor industry. Thus, there remains a need for alternativepolishing systems and methods of polishing substrates comprising siliconcarbide.

BRIEF SUMMARY OF THE INVENTION

The invention provides a method of chemically-mechanically polishing asubstrate, which method comprises (i) contacting a substrate comprisingat least one layer of single crystal silicon carbide with achemical-mechanical polishing composition comprising (a) a liquidcarrier, (b) an abrasive suspended in the liquid carrier, wherein theabrasive is substantially spherical silica particles having an averageparticle size of about 40 nm to about 130 nm, and (c) an oxidizing agentselected from the group consisting of hydrogen peroxide, oxone, ammoniumcerium nitrate, periodates, iodates, persulfates, and mixtures thereof,(ii) moving the polishing composition relative to the substrate, and(iii) abrading at least a portion of the silicon carbide of thesubstrate to polish the substrate.

The invention further provides a method of chemically-mechanicallypolishing a substrate, which method comprises (i) contacting a substratecomprising at least one layer of single crystal silicon carbide with achemical-mechanical polishing composition comprising (a) a liquidcarrier, (b) an abrasive suspended in the liquid carrier, wherein theabrasive is alumina and is present in an amount of about 3 wt. % or lessbased on the weight of the liquid carrier and any components dissolvedor suspended therein, and (c) an oxidizing agent, wherein the oxidizingagent is present in an amount of about 0.001 wt. % to about 0.5 wt. %based on the weight of the liquid carrier and any components dissolvedor suspended therein, and is selected from the group consisting ofhydrogen peroxide, oxone, ammonium cerium nitrate, periodates, iodates,persulfates, and mixtures thereof, and (ii) moving the polishingcomposition relative to the substrate, and (iii) abrading at least aportion of the silicon carbide of the substrate to polish the substrate.

The invention also provides a method of chemically-mechanicallypolishing a substrate, which method comprises (i) contacting a substratecomprising at least one layer of silicon carbide with achemical-mechanical polishing composition comprising (a) a liquidcarrier, (b) an abrasive suspended in the liquid carrier, and (c) anoxidizing agent, wherein the oxidizing agent is present in an amount ofabout 0.001 wt. % to about 0.5 wt. % based on the weight of the liquidcarrier and any components dissolved or suspended therein, and isselected from the group consisting of oxone, potassium persulfate, andmixtures thereof (ii) moving the polishing composition relative to thesubstrate, and (iii) abrading at least a portion of the silicon carbideof the substrate to polish the substrate.

The invention additionally provides a method of chemically-mechanicallypolishing a substrate, which method comprises (i) contacting a substratecomprising at least one layer of single crystal silicon carbide with achemical-mechanical polishing composition comprising (a) a liquidcarrier, (b) an abrasive suspended in the liquid carrier, wherein theabrasive is alumina and is present in an amount of about 3 wt. % or lessbased on the weight of the liquid carrier and any components dissolvedor suspended therein, and (c) an oxidizing agent, wherein the oxidizingagent is present in an amount of about 0.001 wt. % to about 2.5 wt. %based on the weight of the liquid carrier and any component dissolved orsuspended therein, wherein the oxidizing agent is selected from thegroup consisting of hydrogen peroxide, oxone, ammonium cerium nitrate,periodates, periodic acid, iodates, persulfates, chromates,permanganates, bromates, perbromates, ferrates, perrhenates,perruthenates, and mixtures thereof, and (ii) moving the polishingcomposition relative to the substrate, and (iii) abrading at least aportion of the silicon carbide of the substrate to polish the substrate.

The invention further provides a method of chemically-mechanicallypolishing a substrate, which method comprises (i) contacting a substratecomprising at least one layer of single crystal silicon carbide with achemical-mechanical polishing composition comprising (a) a liquidcarrier, (b) an abrasive suspended in the liquid carrier, wherein theabrasive is selected from the group consisting of alumina, titania,ceria, and zirconia, and wherein the abrasive is present in an amount ofabout 3 wt. % or less based on the weight of the liquid carrier and anycomponents dissolved or suspended therein, and (c) a permanganate salt,wherein the permanganate salt is present in an amount of about 0.001 wt.% to about 2.5 wt. % based on the weight of the liquid carrier and anycomponents dissolved or suspended therein, (ii) moving the polishingcomposition relative to the substrate, and (iii) abrading at least aportion of the silicon carbide of the substrate to polish the substrate.

The invention also provides a method of chemically-mechanicallypolishing a substrate, which method comprises (i) contacting a substratecomprising at least one layer of single crystal silicon carbide with achemical-mechanical polishing composition comprising (a) a liquidcarrier, (b) an abrasive suspended in the liquid carrier, wherein theabrasive is selected from the group consisting of alumina, titania,ceria, and zirconia, and wherein the abrasive is present in an amount ofabout 3 wt. % or less based on the weight of the liquid carrier and anycomponents dissolved or suspended therein, and (c) periodic acid orperiodates, wherein the periodic acid or periodates is present in anamount of about 0.001 wt. % to about 1 wt. % based on the weight of theliquid carrier and any components dissolved or suspended therein, (ii)moving the polishing composition relative to the substrate, and (iii)abrading at least a portion of the silicon carbide of the substrate topolish the substrate.

DETAILED DESCRIPTION OF THE INVENTION

The invention provides a method of chemically-mechanically polishing asubstrate comprising silicon carbide. The method comprises (i)contacting a substrate comprising at least one layer of single crystalsilicon carbide, (ii) moving the polishing composition relative to thesubstrate, and (iii) abrading at least a portion of the silicon carbideof the substrate to polish the substrate. The polishing compositioncomprises, consists essentially of, or consists of (a) a liquid carrier,(b) an abrasive suspended in the liquid carrier, and (c) an oxidizingagent.

In a first embodiment, the abrasive is substantially spherical silicaparticles having an average particle size of about 40 nm to about 130nm, and the oxidizing agent is selected from the group consisting ofhydrogen peroxide, oxone, ammonium cerium nitrate, periodates, iodates,persulfates, and mixtures thereof. In a second embodiment, the abrasiveis alumina and is present in an amount of about 3 wt. % or less based onthe weight of the liquid carrier and any components dissolved orsuspended therein, and the oxidizing agent is present in an amount ofabout 0.001 wt. % to about 0.5 wt. % based on the weight of the liquidcarrier and any components dissolved or suspended therein, and isselected from the group consisting of hydrogen peroxide, oxone, ammoniumcerium nitrate, periodates, iodates, persulfates, and mixtures thereof.In a third embodiment, the oxidizing agent is present in an amount ofabout 0.001 wt. % to about 0.5 wt. % based on the weight of the liquidcarrier and any components dissolved or suspended therein, and isselected from the group consisting of oxone, potassium persulfate, andmixtures thereof. In a fourth embodiment, the abrasive is alumina and ispresent in an amount of about 3 wt. % or less based on the weight of theliquid carrier and any components dissolved or suspended therein, andthe oxidizing agent is present in an amount of about 0.001 wt. % toabout 0.5 wt. % based on the weight of the liquid carrier and anycomponents dissolved or suspended therein, and is selected from thegroup consisting of hydrogen peroxide, oxone, ammonium cerium nitrate,periodates, periodic acid, iodates, persulfates, chromates,permanganates, bromates, perbromates, ferrates, perrhenates,perruthenates, and mixtures thereof. In a fifth embodiment, the abrasiveis alumina, titania, ceria, or zirconia, and is present in an amount ofabout 3 wt. % or less based on the weight of the liquid carrier and anycomponents dissolved or suspended therein, and the oxidizing agent is apermanganate salt, wherein the permanganate salt is present in an amountof about 0.001 wt. % to about 2.5 wt. % based on the weight of theliquid carrier and any components dissolved or suspended therein. In asixth embodiment, the abrasive is alumina, titania, ceria, or zirconia,and is present in an amount of about 3 wt. % or less based on the weightof the liquid carrier and any components dissolved or suspended therein,and the oxidizing agent is periodic acid, wherein the periodic acid ispresent in an amount of about 0.001 wt. % to about 1 wt. % based on theweight of the liquid carrier and any components dissolved or suspendedtherein.

The substrate to be polished using the method of the invention can beany suitable substrate which comprises at least one layer of siliconcarbide. Suitable substrates include, but are not limited to, flat paneldisplays, integrated circuits, memory or rigid disks, metals, interlayerdielectric (ILD) devices, semiconductors, micro-electro-mechanicalsystems, ferroelectrics, and magnetic heads. The silicon carbide cancomprise, consist essentially of, or consist of any suitable siliconcarbide, many of which are known in the art. The silicon carbide can besingle crystal or polycrystalline. Silicon carbide has many differenttypes of crystal structures, each having its own distinct set ofelectronic properties. Only a small number of these polytypes, however,can be reproduced in a form acceptable for use as semiconductors. Suchpolytypes can be either cubic (e.g., 3C silicon carbide) or non-cubic(e.g., 4H silicon carbide, 6H silicon carbide). The properties of thesepolytypes are well known in the art.

The polishing pad can be any suitable polishing pad, many of which areknown in the art. Suitable polishing pads include, for example, wovenand non-woven polishing pads. Moreover, suitable polishing pads cancomprise any suitable polymer of varying density, hardness, thickness,compressibility, ability to rebound upon compression, and compressionmodulus. Suitable polymers include, for example, polyvinylchloride,polyvinylfluoride, nylon, fluorocarbon, polycarbonate, polyester,polyacrylate, polyether, polyethylene, polyamide, polyurethane,polystyrene, polypropylene, conformed products thereof, and mixturesthereof.

The polishing pad can comprise fixed abrasive particles on or within thepolishing surface of the polishing pad, or the polishing pad can besubstantially free of fixed abrasive particles. Fixed abrasive polishingpads include pads having abrasive particles affixed to the polishingsurface of the polishing pad by way of an adhesive, binder, ceramer,resin, or the like or abrasives that have been impregnated within apolishing pad so as to form an integral part of the polishing pad, suchas, for example, a fibrous batt impregnated with an abrasive-containingpolyurethane dispersion.

The polishing pad can have any suitable configuration. For example, thepolishing pad can be circular and, when in use, typically will have arotational motion about an axis perpendicular to the plane defined bythe surface of the pad. The polishing pad can be cylindrical, thesurface of which acts as the polishing surface, and, when in use,typically will have a rotational motion about the central axis of thecylinder. The polishing pad can be in the form of an endless belt,which, when in use, typically will have a linear motion with respect tothe cutting edge being polished. The polishing pad can have any suitableshape and, when in use, have a reciprocating or orbital motion along aplane or a semicircle. Many other variations will be readily apparent tothe skilled artisan.

The polishing composition comprises an abrasive, which desirably issuspended in the liquid carrier (e.g., water). The abrasive typically isin particulate form. Any suitable abrasive can be used, many of whichare well known in the art. Preferably, the abrasive comprises, consistsessentially of, or consists of one or more metal oxides. The metal oxidedesirably is selected from the group consisting of alumina, ceria,germania, magnesia, silica, titania, zirconia, co-formed productsthereof, and combinations thereof.

In particular, the abrasive comprises, consists essentially of, orconsists of substantially spherical silica, alumina, ceria, zirconia, ortitania. Substantially spherical silica is also referred to as colloidalsilica by those of ordinary skill in the art. Preferably, thesubstantially spherical silica is precipitated orcondensation-polymerized silica, which is prepared using the sol-gelprocess. Condensation-polymerized silica particles typically areprepared by condensing Si(OH)₄ to form substantially sphericalparticles. The precursor Si(OH)₄ can be obtained, for example, byhydrolysis of high purity alkoxysilanes, or by acidification of aqueoussilicate solutions. Such abrasive particles can be prepared inaccordance with U.S. Pat. No. 5,230,833 or can be obtained as any ofvarious commercially available products such as Bindzil from EKAChemicals, the Fuso PL-1, PL-2, and PL-3 products, and the Nalco 1034A,1050, 2327, and 2329 products, as well as other similar productsavailable from DuPont, Bayer, Applied Research, Nissan Chemical, andClariant. Preferably, the alumina is seeded gel process alpha alumina,which is available from manufactures such as Saint Gobain (alphaalumina). The substantially spherical silica, alumina, ceria, zirconia,and titania particles can have any suitable particle size. For example,the substantially spherical silica, alumina, ceria, zirconia, andtitania particles can have an average particle size of about 10 nm ormore (e.g., about 20 nm or more, about 30 nm or more, about 40 nm ormore, or about 50 nm or more). The substantially spherical silica,alumina, ceria, zirconia, and titania particles can have an averageparticle size of about 200 nm or less (e.g., about 180 nm or less, about170 nm or less, about 160 nm or less, about 150 nm or less, about 130 nmor less, about 110 nm or less, or about 100 nm or less). Accordingly,the substantially spherical silica, alumina, ceria, zirconia, andtitania particles can have an average particle size of about 40 nm toabout 130 nm (e.g., about 45 μm to about 125 nm, about 50 nm to about120 nm, about 55 nm to about 115 nm, or about 60 nm to about 110 nm).The particle size of a particle is the diameter of the smallest spherethat encompasses the particle.

Any suitable amount of abrasive can be present in the polishingcomposition. Typically, about 0.01 wt. % or more (e.g., about 0.05 wt. %or more) abrasive will be present in the polishing composition. Moretypically, about 0.1 wt. % or more (e.g., about 1 wt. % or more, about 5wt. % or more, about 7 wt. % or more, about 10 wt. % or more, or about12 wt. % or more) abrasive will be present in the polishing composition.The amount of abrasive in the polishing composition typically will beabout 50 wt. % or less, more typically will be about 40 wt. % or less(e.g., about 15 wt. % or less, about 10 wt. % or less, about 5 wt. % orless, about 3 wt. % or less, about 1 wt. % or less, about 0.6 wt. % orless, or about 0.3 wt. % or less). Accordingly, the amount of abrasivein the polishing composition can be about 2 wt. % to about 50 wt. %, andmore preferably about 5 wt. % to about 40 wt. % (e.g., about 10 wt. % toabout 35 wt. %, about 15 wt. % to about 35 wt. %, or about 20 wt. % toabout 35 wt. %). The amount of abrasive in the polishing compositionalso can be about 0.01 wt. % to about 3 wt. % (e.g., about 0.05 wt. % toabout 1 wt. % or about 0.1 wt. % to about 0.6 wt. %).

A liquid carrier is used to facilitate the application of the abrasiveand any optional additives to the surface of a suitable substrate to bepolished (e.g., planarized). The liquid carrier can be any suitableliquid, e.g., solvent, including lower alcohols (e.g., methanol,ethanol, etc.), ethers (e.g., dioxane, tetrahydrofuran, etc.), water,and mixtures thereof. Preferably, the liquid carrier comprises, consistsessentially of, or consists of water, more preferably deionized water.

The polishing composition comprises an oxidizing agent, which can be anysuitable oxidizing agent for one or more materials of the substrate tobe polished with the polishing composition. Preferably, the oxidizingagent is selected from the group consisting of hydrogen peroxide, oxone,ammonium cerium nitrate, periodates, iodates, persulfates, chlorates,chromates, permanganates, bromates, perbromates, ferrates, perrhenates,perruthenates, and mixtures thereof. The permanganates, periodates, andpersulfates can be any periodate, iodate, persulfate or combination ofperiodates, iodates, and persulfates, such as, for example, potassiumperiodate, periodic acid, ammonium persulfate, potassium persulfate, orpotassium permanganate. More preferably, the oxidizing agent is oxone,potassium persulfate, potassium permanganate, or periodic acid. Theoxidizing agent can be present in the polishing composition in anysuitable amount. Typically, the polishing composition comprises about0.001 wt. % or more (e.g., about 0.005 wt. % or more, about 0.01 wt. %or more, about 0.05 wt. % or more, or about 0.1 wt. % or more) oxidizingagent. The polishing composition preferably comprises about 20 wt. % orless (e.g., about 15 wt. % or less, about 10 wt. % or less, about 5 wt.% or less, about 2.5 wt. % or less, about 2 wt. % or less, about 1 wt. %or less, or about 0.5 wt. % or less) oxidizing agent. Preferably, thepolishing composition comprises about 0.001 wt. % to about 20 wt. %(e.g., about 0.001 wt. % to about 15 wt. %, about 0.001 wt. % to about2.5 wt. %, about 0.005 wt. % to about 10 wt. %, about 0.01 wt. % toabout 5 wt. %, about 0.05 wt. % to about 2 wt. %, or about 0.1 wt. % toabout 0.5 wt. %) oxidizing agent. More preferably, the polishingcomposition comprises about 0.001 wt. % to about 0.05 wt. %, about 0.001wt. % to about 0.1 wt. %, about 0.001 wt. % to about 0.5 wt. %, or about0.001 wt. % to about 2 wt. % oxidizing agent.

The polishing composition, specifically the liquid carrier with anycomponents dissolved or suspended therein, can have any suitable pH. Theactual pH of the polishing composition will depend, in part, on the typeof substrate being polished. The polishing composition can have a pH ofabout 11 or less (e.g., about 9 or less, about 7 or less, about 6 orless, about 5 or less, about 4 or less, about 3 or less, or about 2 orless). The polishing composition can have a pH of about 1 or more (e.g.,about 2 or more, about 3 or more, about 4 or more, about 6 or more,about 8 or more, or about 9 or more). The pH can be, for example, fromabout 1 to about 11 (e.g., from about 2 to about 10, from about 2 toabout 6, from about 3 to about 9, from about 4 to about 8, from about 5to about 7, or from about 3 to about 5).

The pH of the polishing composition can be achieved and/or maintained byany suitable means. More specifically, the polishing composition canfurther comprise a pH adjustor, a pH buffering agent, or a combinationthereof. The pH adjustor can comprise, consist essentially of, orconsist of any suitable pH-adjusting compound. For example, the pHadjustor can be any suitable acid, such as an inorganic or an organicacid, or combination thereof. For example, the acid can be nitric acid.The pH buffering agent can be any suitable buffering agent, for example,phosphates, acetates, borates, sulfonates, carboxylates, and the like.The polishing composition can comprise any suitable amount of a pHadjustor and/or a pH buffering agent, provided such amount is sufficientto achieve and/or maintain the desired pH of the polishing composition,e.g., within the ranges set forth herein.

It will be appreciated that many of the aforementioned compounds canexist in the form of a salt, an acid, or as a partial salt. Furthermore,certain compounds or reagents may perform more than one function. Forexample, some compounds can function both as a chelating agent and anoxidizing agent.

The polishing composition can comprise a surfactant and/or rheologicalcontrol agent, including viscosity enhancing agents and coagulants(e.g., polymeric rheological control agents, such as, for example,urethane polymers). Suitable surfactants can include, for example,cationic surfactants, anionic surfactants, nonionic surfactants,amphoteric surfactants, mixtures thereof, and the like. The amount ofsurfactant in the polishing composition typically is about 0.0001 wt. %to about 1 wt. % (preferably about 0.001 wt. % to about 0.1 wt. % andmore preferably about 0.005 wt. % to about 0.05 wt. %).

The polishing composition can comprise an antifoaming agent. Theantifoaming agent can be any suitable anti-foaming agent. Suitableantifoaming agents include, but are not limited to, silicon-based andacetylenic diol-based antifoaming agents. The amount of anti-foamingagent in the polishing composition typically is about 10 ppm to about140 ppm.

The polishing composition can comprise a biocide. The biocide can be anysuitable biocide, for example, an isothiazolinone biocide. The amount ofbiocide in the polishing composition typically is about 1 to about 50ppm, preferably about 10 to about 20 ppm.

The polishing composition can be prepared by any suitable technique,many of which are known to those skilled in the art. The polishingcomposition can be prepared in a batch or continuous process. Generally,the polishing composition can be prepared by combining the componentsthereof in any order. The term “component” as used herein includesindividual ingredients (e.g., oxidizing agent, abrasive, etc.) as wellas any combination of ingredients (e.g., water, halogen anion,surfactants, etc.).

The polishing composition can be supplied as a one-package systemcomprising the liquid carrier, the abrasive, the oxidizing agent, andoptionally other additives. Alternatively, some of the components, suchas an oxidizing agent, can be supplied in a first container, either indry form, or as a solution or dispersion in the liquid carrier, and theremaining components, such as the abrasive and other additives, can besupplied in a second container or multiple other containers. Othertwo-container, or three or more container combinations of the componentsof the polishing composition are within the knowledge of one of ordinaryskill in the art.

Solid components, such as the abrasive, can be placed in one or morecontainers either in dry form or as a solution in the liquid carrier.Moreover, it is suitable for the components in the first, second, orother containers to have different pH values, or alternatively to havesubstantially similar, or even equal, pH values. The components of thepolishing composition can be partially or entirely supplied separatelyfrom each other and can be combined, e.g., by the end-user, shortlybefore use (e.g., 1 week or less prior to use, 1 day or less prior touse, 1 hour or less prior to use, 10 minutes or less prior to use, or 1minute or less prior to use).

The polishing composition also can be provided as a concentrate which isintended to be diluted with an appropriate amount of liquid carrierprior to use. In such an embodiment, the polishing compositionconcentrate can comprise a liquid carrier and optionally othercomponents in amounts such that, upon dilution of the concentrate withan appropriate amount of liquid carrier, each component will be presentin the polishing composition in an amount within the appropriate rangerecited above for each component. For example, each component can bepresent in the concentrate in an amount that is about 2 times (e.g.,about 3 times, about 4 times, or about 5 times) greater than theconcentration recited above for each component in the polishingcomposition so that, when the concentrate is diluted with an appropriatevolume of liquid carrier (e.g., an equal volume of liquid carrier, 2equal volumes of liquid carrier, 3 equal volumes of liquid carrier, or 4equal volumes of liquid carrier, respectively), each component will bepresent in the polishing composition in an amount within the ranges setforth above for each component. Furthermore, as will be understood bythose of ordinary skill in the art, the concentrate can contain anappropriate fraction of the liquid carrier present in the finalpolishing composition in order to ensure that the other components ofthe polishing composition are at least partially or fully dissolved orsuspended in the concentrate.

The inventive method of polishing a substrate is particularly suited foruse in conjunction with a chemical-mechanical polishing (CMP) apparatus.Typically, the apparatus comprises a platen, which, when in use, is inmotion and has a velocity that results from orbital, linear, or circularmotion, a polishing pad in contact with the platen and moving with theplaten when in motion, and a carrier that holds a substrate to bepolished by contacting and moving relative to the surface of thepolishing pad. The polishing of the substrate takes place by thesubstrate being placed in contact with the polishing pad and thepolishing composition (which generally is disposed between the substrateand the polishing pad), with the polishing pad moving relative to thesubstrate, so as to abrade at least a portion of the substrate to polishthe substrate.

Desirably, the polishing end-point is determined by monitoring theweight of the silicon carbide substrate, which is used to compute theamount silicon carbide removed from the substrate. Such techniques arewell known in the art.

Polishing refers to the removal of at least a portion of a surface topolish the surface. Polishing can be performed to provide a surfacehaving reduced surface roughness by removing gouges, crates, pits, andthe like, but polishing also can be performed to introduce or restore asurface geometry characterized by an intersection of planar segments.

The method of the invention can be used to polish any suitable substratecomprising at least one layer of silicon carbide. The silicon carbidecan be removed at any suitable rate to effect polishing of thesubstrate. For example, silicon carbide can be removed at a rate ofabout 5 nm/hr or more (e.g., about 10 nm/hr or more, about 20 nm/hr ormore, about 50 nm/hr or more, about 70 nm/hr or more, about 100 nm/hr ormore, or about 200 nm/hr or more). The silicon carbide can be removed ata rate of about 800 nm/hr or less (e.g., about 500 nm/hr or less, about300 nm/hr or less, about 250 nm/hr or less, or about 200 nm/hr or less).Accordingly, the silicon carbide can be removed from the substrate at arate of about 5 nm/hr to about 1500 nm/hr (e.g., about 10 nm/hr to about1000 nm/hr, about 20 nm/hr to about 800 nm/hr, about 30 nm/hr to about500 nm/hr, about 40 nm/hr to about 300 nm/hr, or about 50 nm/hr to about180 nm/hr). More preferably, the silicon carbide can be removed from thesubstrate at a rate of about 20 nm/hr to about 180 nm/hr, about 70 nm/hrto about 180 nm/hr, about 100 nm/hr to about 180 nm/hr, about 30 nm/hrto about 2700 nm/hr, about 30 nm/hr to about 1000 nm/hr, about 100 nm/hrto about 500 nm/hr, or about 200 nm/hr to about 400 nm/hr.

The following examples further illustrate the invention but, of course,should not be construed as in any way limiting its scope.

EXAMPLE 1

This example demonstrates the effect on the removal rate of siliconcarbide by the presence of substantially spherical silica and anoxidizer in a polishing composition.

A 6H semi-insulating single crystal silicon carbide wafer was polishedwith ten different polishing compositions. The contents and pH of eachof the polishing compositions are indicated in Table 1. The siliconcarbide removal rate (nm/hr) was determined for each polishingcomposition, and the results are shown in Table 1.

TABLE 1 Polishing Abrasive Oxidizer Silicon Carbide Removal CompositionConcentration Concentration pH Rate (nm/hr) 1A (comparative) 30 wt. %fumed N/A 10-10.5 0 silica 1B (comparative) 30 wt. % fumed 0.5 wt. %H₂O₂ 10-10.5 46.5 silica 1C (comparative) 30 wt. % fumed 1.0 wt. % H₂O₂10-10.5 77.5 silica 1D (comparative) 30 wt. % fumed 2.0 wt. % H₂O₂10-10.5 69.75 silica 1E (comparative) 30 wt. % N/A 10 0 substantiallyspherical silica 1F (invention) 30 wt. % 1 wt. % 10 77.5 substantiallyammonium spherical silica persulfate 1G (invention) 30 wt. % 1 wt. % 1093 substantially ammonium spherical silica persulfate 1H (invention) 30wt. % 1 wt. % KIO₃ 11 124 substantially spherical silica 1I (invention)30 wt. % 2 wt. % 10 124 substantially ammonium spherical silicapersulfate 1J (invention) 30 wt. % 2 wt. % oxone 10 93 substantiallyspherical silica

As is apparent from the data presented in Table 1, the silicon carbideremoval rate increases when the polishing composition comprisessubstantially spherical silica particles in combination with anoxidizing agent such as ammonium persulfate, potassium iodate, or oxone.

EXAMPLE 2

This example demonstrates the effect on the removal rate of siliconcarbide by the presence of different oxidizing agents in the polishingcomposition of the invention.

A 4HN single crystal silicon carbide wafer was polished with sevendifferent polishing compositions. Each of the polishing compositionscontained 30 wt. % substantially spherical silica. Six of the polishingcompositions were further modified by the addition of either ammoniumpersulfate or ammonium cerium nitrates as indicated in Table 2.

The silicon carbide removal rate (nm/hr) was determined for eachpolishing composition, and the results are shown in Table 2.

TABLE 2 Polishing Oxidizer Silicon Carbide Composition Concentration pHRemoval Rate (nm/hr) 2A (comparative) N/A 10 0 2B (invention) 1 wt. % 10105 ammonium persulfate 2C (invention) 1 wt. % 10 87.5 ammoniumpersulfate 2D (invention) 1 wt. % 10 126 ammonium persulfate 2E(invention) 1 wt. % 10 182 ammonium persulfate 2F (invention) 2 wt. % 10105 ammonium persulfate 2G (invention) 1 wt. % 1.7 126 ammonium ceriumnitrate

As is apparent from the data presented in Table 2, the presence ofeither ammonium persulfate or ammonium cerium nitrate in the polishingcomposition increased the silicon carbide removal rate from 0 to as highas 182 nm/hr.

EXAMPLE 3

This example demonstrates the effect on the removal rate of siliconcarbide by the presence of an oxidizer in a polishing composition.

A 4H semi-insulating single crystal silicon carbide wafer was polishedwith three different polishing compositions. Each of the polishingcompositions contained 30 wt. % substantially spherical silica and wasadjusted to a pH of 10. Two of the polishing compositions were furthermodified by the addition of ammonium persulfate as indicated in Table 3.

The silicon carbide removal rate (nm/hr) was determined for eachpolishing composition, and the results are shown in Table 3.

TABLE 3 Polishing Oxidizer Silicon Carbide Composition ConcentrationRemoval Rate (nm/hr) 3A (comparative) N/A 0 3B (invention) 1 wt. % 22.75ammonium persulfate 3C (invention) 1 wt. % 21 ammonium persulfate

As is apparent from the data presented in Table 3, the silicon carbideremoval rate increases when the polishing composition comprises ammoniumpersulfate.

EXAMPLE 4

This example demonstrates the effect on the removal rate of siliconcarbide by the presence of an oxidizer and an abrasive in a polishingcomposition.

A 4H single crystal silicon carbide wafer was polished with fifteendifferent polishing compositions. The contents and pH of each of thepolishing compositions are indicated below in Table 4. The siliconcarbide removal rate (nm/hr) was determined for each polishingcomposition, and the results are shown in Table 4.

TABLE 4 Silicon Carbide Polishing Abrasive Removal Rate CompositionConcentration pH Oxidizer Concentration (nm/hr) 4A (comparative) 20 wt.% 10 N/A 76 substantially spherical silica (Bindzil) 4B (invention) 20wt. % 10 0.5 wt. % H₂O₂ 105 substantially spherical silica (Bindzil) 4C(invention) 20 wt. % 10 0.5 wt. % potassium 102 substantially periodatespherical silica (Bindzil) 4D (invention) 20 wt. % 10 0.5 wt. %potassium 104 substantially persulfate spherical silica (Bindzil) 4E(comparative) 20 wt. % 2 N/A 97 substantially spherical silica (Nalco1034) 4F (comparative) 20 wt. % 2 0.5 wt. % H₂O₂ 96 substantiallyspherical silica (Nalco 1034) 4G (invention) 20 wt. % 2 0.5 wt. %potassium 122 substantially periodate spherical silica (Nalco 1034) 4H(invention) 20 wt. % 2 0.5 wt. % potassium 116 substantially persulfatespherical silica (Nalco 1034) 4I (comparative) 0.5 wt. % ceria 5 N/A 04K (comparative) 0.5 wt. % ceria 5 3000 ppm potassium 0 periodate 4L(invention) 0.5 wt. % ceria 5 3000 ppm potassium 64 persulfate 4M(comparative) 7.5 wt. % g seeded 3 N/A 0 gel process alpha alumina 4N(invention) 7.5 wt. % seeded 3 0.5 wt. % H₂O₂ 37 gel process alphaalumina 4O (invention) 7.5 wt. % seeded 3 0.5 wt. % potassium 59 gelprocess alpha periodate alumina 4P (invention) 7.5 wt. % seeded 3 0.5wt. % potassium 350 gel process alpha persulfate alumina

As is apparent from the data presented in Table 4, the silicon carbideremoval rate typically increases upon the addition of an oxidizer to thepolishing composition. The combination of seeded gel process alphaalumina with potassium persulfate was particularly effective inincreasing the removal rate of silicon carbide.

EXAMPLE 5

This example demonstrates the effect on the removal rate of siliconcarbide by the presence of different types of alumina abrasive in apolishing composition.

A 4H single crystal silicon carbide wafer was polished with sixdifferent polishing compositions. Each of the polishing compositionscontained 3 wt. % abrasive and 1.0 wt. % potassium persulfate, and wasadjusted to a pH of 3. The type of alumina abrasive used in each of thepolishing compositions is indicated below in Table 5.

The silicon carbide removal rate (nm/hr) was determined for eachpolishing composition, and the results are shown in Table 5.

TABLE 5 Silicon Carbide Polishing Alumina Average Particle Removal RateComposition Alumina Type Manufacturer Size (nm) (nm/hr) 5A (invention)seeded gel Saint Gobain <100 315 process alpha (alpha) 5B (invention)fumed Degussa 120 109 (RMU3-11) 5C (invention) fumed Cabot (RMWA- 120129 11) 5D (invention) polymer coated Cabot 120 58 aluminaMicroelectronics (TPA6) 5E (invention) alpha Saint Gobain PN 350 1217955.35 5F (invention) alpha Saint Gobain PN 800 151 7955.80

As is apparent from the data presented in Table 5, use of the seeded gelprocess alpha alumina resulted in a silicon carbide removal rate whichwas significantly larger than the rates achieved with the compositionscontaining other types of alumina.

EXAMPLE 6

This example demonstrates the effect on the removal rate of siliconcarbide by the concentration of potassium persulfate in a polishingcomposition.

A 4HN single crystal silicon carbide wafer was polished with fivedifferent polishing compositions. Each of the polishing compositionscontained 3 wt. % seeded gel process alpha alumina and was adjusted to apH of 4. Four of the polishing compositions were further modified by theaddition of potassium persulfate.

The silicon carbide removal rate (nm/hr) was determined for eachpolishing composition, and the results are shown in Table 6.

TABLE 6 Potassium Persulfate Silicon Carbide Polishing ConcentrationColloidal Removal Rate Composition (wt. %) Stability (nm/hr) 6A(comparative) 0 stable 15 6B (invention) 0.002 stable 290 6C (invention)0.005 stable 336 6D (invention) 0.03 stable 270 6E (invention) 0.1unstable 288

As is apparent from the data presented in Table 6, the silicon carbideremoval rate continued to increase as the concentration of potassiumpersulfate increased up to a concentration between 0.005 wt. % and 0.03wt. % potassium persulfate.

EXAMPLE 7

This example demonstrates the effect on the removal rate of siliconcarbide by the concentration of seeded gel process alpha alumina in apolishing composition.

A 4HN single crystal silicon carbide wafer was polished with twodifferent polishing compositions. Each of the polishing compositionscontained 0.1 wt. % potassium persulfate and was adjusted to a pH of 4.The polishing compositions also contained seeded gel process alphaalumina at a concentration of either 0.1 wt. % or 0.5 wt. %.

The silicon carbide removal rate (nm/hr) was determined for eachpolishing composition, and the results are shown in Table 7.

TABLE 7 Alumina Silicon Carbide Polishing Concentration Removal RateComposition (wt. %) (nm/hr) 7A (invention) 0.1 213 7B (invention) 0.5288

As is apparent from the data presented in Table 7, although bothcompositions were effective in polishing the silicon carbide wafer, thecomposition containing the higher concentration of alumina achieved ahigher silicon carbide polishing rate.

EXAMPLE 8

This example demonstrates the effect on the removal rate of severaldifferent types of silicon carbide wafers by a polishing composition.

Nine different types of single crystal silicon carbide wafers werepolished with a polishing composition containing 0.6 wt. % seeded gelprocess alpha alumina and 0.03 wt. % potassium persulfate, adjusted to apH of 4.

The silicon carbide removal rate (nm/hr) was determined for each type ofwafer, and the results are shown in Table 8.

TABLE 8 Silicon Carbide Removal Rate Silicon Carbide Wafer Type (nm/br)4HN single crystal 282 6H semi-insulating 235 6H semi-insulating 222 6Hsemi-insulating 241 4HN single crystal 322 6H semi-insulating 341 6Hsemi-insulating 358 6H semi-insulating 345 4HN single crystal 316

As is apparent from the data presented in Table 8, the inventivepolishing composition was able to successfully polish each type ofsilicon carbide wafer tested.

EXAMPLE 9

This example demonstrates the effect on the removal rate of siliconcarbide by polishing a silicon carbide substrate using different polishtool parameters with a polishing composition.

Five different sets of polishing tool parameters were used to polish achemical vapor deposition (CVD) polycrystalline silicon carbide waferwith a polishing composition containing 1 wt. % seeded gel process alphaalumina and 0.3 wt. % potassium persulfate, adjusted to a pH of 4.

The silicon carbide removal rate (nm/hr) was determined for each set ofpolishing conditions, and the results are shown in Table 9.

TABLE 9 Silicon Carbide Polishing Platen Speed Down Force Removal RateConditions (rpm) (kPa) [psi] (nm/hr) 9A (invention) 60  6.62 [0.96] 639B (invention) 60 19.97 [2.87] 221 9C (invention) 100 19.97 [2.87] 6559D (invention) 120 32.96 [4.78] 978 9E (invention) 120 32.96 [4.78] 982

As is apparent from the data presented in Table 9, the silicon carbideremoval rate increased as the platen rotational speed of the polishingpad and the down force pressure of the substrate against the polishingpad were increased.

EXAMPLE 10

This example demonstrates the effect on the removal rate of siliconcarbide by the presence of different oxidizing agents in the polishingcomposition of the invention.

A 4H semi-insulating single crystal silicon carbide wafer was polishedwith 12 different polishing compositions. Each of the polishingcompositions contained 0.6 wt. % seeded gel process alpha alumina andwas adjusted to a pH of 4.

The silicon carbide removal rate (nm/hr) was determined for eachpolishing composition, and the results are shown in Table 10.

TABLE 10 Silicon Carbide Removal Rate Polishing Composition OxidizerConcentration (nm/hr) 10A (invention) 0.3 wt. % potassium persulfate280-313 10B (invention) 0.12 wt. % potassium permanganate 1682 10C(invention) 0.27 wt. % potassium chlorate 152 10D (comparative) 0.48 wt.% cerium perchlorate <10 10E (invention) 0.43 wt. % potassium chromate492 10F (invention) 0.43 wt. % ammonium iodate 20 10G (invention) 0.25wt. % periodic acid 694 10H (invention) 0.37 wt. % potassium bromate 23610I (comparative) Iodine <10 10J (invention) 0.3 wt. % potassiumpersulfate and 473 0.12 wt. % potassium permanganate 10K (comparative)0.37 wt. % sodium tungstate <10 dehydrate 10L (comparative) 0.26 wt. %potassium molybdate <10

As is apparent from the data presented in Table 10, the silicon carbideremoval rate increases when the polishing composition comprises aluminaparticles in combination with an oxidizing agent such as potassiumpersulfate, potassium permanganate, potassium chlorate, potassiumchromate, periodic acid, or potassium bromate.

EXAMPLE 11

This example demonstrates the effect on the removal rate of siliconcarbide by the concentration of potassium permanganate in a polishingcomposition.

A 4H semi-insulating single crystal silicon carbide wafer was polishedwith 11 different polishing compositions. Each of the polishingcompositions contained 0.6 wt. % seeded gel process alpha alumina.

The silicon carbide removal rate (nm/hr) was determined for eachpolishing composition, and the results are shown in Table 11.

TABLE 11 Potassium Silicon Carbide Polishing Permangante Removal RateComposition Concentration (wt. %) pH (nm/hr) 11A (invention) 0.1 4 166011B (invention) 0.12 4 1682 11C (invention) 0.14 4 1722 11D (invention)0.18 4 1591 11E (invention) 0.2 4 1712 11F (invention) 0.3 4 1747 11G(invention) 0.5 4 1922 11H (invention) 1.0 4 1958 11I (invention) 1.5 41812 11J (invention) 2.5 4 1913 11K (invention) 0.14 10 164

As is apparent from the data presented in Table 11, polishingcompositions comprising potassium permanganate over a concentrationrange of 14 wt. % to 2.5 wt. % and at pH of about 4 resulted in asignificant silicon carbide removal rate.

EXAMPLE 12

This example demonstrates the effect on the removal rate of siliconcarbide by the concentration of periodic acid and abrasive in apolishing composition and the pH of the polishing composition.

A 4H semi-insulating single crystal silicon carbide wafer was polishedwith 12 different polishing compositions.

The silicon carbide removal rate (nm/hr) was determined for eachpolishing composition, and the results are shown in Table 12.

TABLE 12 Silicon Periodic Acid Alumina Carbide Polishing ConcentrationConcentration Removal Rate Composition pH (wt. %) (wt. %) (nm/hr) 12A(invention) 2 0.15 0.1 504 12B (invention) 2 0.05 0.6 335 12C(invention) 2 0.25 0.6 671 12D (invention) 2 0.15 1.1 761 12E(invention) 4 0.05 0.1 374 12F (invention) 4 0.25 0.1 573 12G(invention) 4 0.15 0.6 717 12H (invention) 4 0.25 1.1 761 12I(invention) 6 0.15 0.1 487 12J (invention) 6 0.05 0.6 586 12K(invention) 6 0.25 0.6 656 12L (invention) 6 0.15 1.1 688

As is apparent from the data presented in Table 12, polishingcompositions comprising periodic acid over a concentration range of 0.05wt. % to 0.25 wt. %, and alpha-alumina over a concentration range of 0.1to 1.1 wt. %, at pH of about 2 to about 6, resulted in a significantsilicon carbide removal rate.

EXAMPLE 13

This example demonstrates the effect on the removal rate of siliconcarbide by the presence of different types of abrasives in a polishingcomposition.

A 4H semi-insulating single crystal silicon carbide wafer was polishedwith 7 different polishing compositions. Each of the polishingcompositions contained an abrasive and potassium permanganate, and wasadjusted to a pH of 4. The type of abrasive used in each of thepolishing compositions and the amount of potassium permanganate areindicated below in Table 13.

The silicon carbide removal rate (nm/hr) was determined for eachpolishing composition, and the results are shown in Table 13.

TABLE 13 Potassium Permangante Abrasive Silicon Carbide PolishingConcentration Concentration Removal Rate Composition (wt. %) AbrasiveType (wt. %) (nm/hr) 13A (invention) 0.12 alpha-alumina 0.6 2069 13B(invention) 0.12 titania 0.6 1032 13C (comparative) 0.12 substantially10 <10 spherical silica (25 nm) 13D (invention) 0.14 zirconia 0.6 38913E (invention) 0.14 ceria 0.6 480 13F (comparative) 0.14 substantially10 70 spherical silica (80 nm) 13G (comparative) 0.14 fumed silica 10 26

As is apparent from the data presented in Table 13, the use ofalpha-alumina, titania, zirconia, and ceria resulted in a siliconcarbide removal rate which was significantly larger than the ratesachieved with the compositions containing silica.

EXAMPLE 14

This example demonstrates the effect on the removal rate of siliconcarbide by the pH of the polishing composition and the concentration ofpotassium permanganate in the polishing composition.

A 4H semi-insulating single crystal silicon carbide wafer was polishedwith 5 different polishing compositions. Each of the polishingcompositions contained 0.6 wt. % ceria and potassium permanganate. ThepH and the amount of potassium permanganate are indicated in Table 14.

The silicon carbide removal rate (nm/hr) was determined for eachpolishing composition, and the results are shown in Table 14.

TABLE 14 Potassium Permangante Polishing Concentration Silicon CarbideComposition (wt. %) pH Removal Rate (nm/hr) 14A (invention) 0.06 2 23314B (invention) 0.25 2 1202 14C (invention) 0.155 4 915 14D (invention)0.06 6 690 14E (invention)) 0.25 6 1907

As is apparent from the data presented in Table 14, the use of ceriaover a pH range of 2 to 6 at a variety of potassium permanganateconcentrations resulted in a significant silicon carbide removal rate.

EXAMPLE 15

This example demonstrates the effect on the removal rate of siliconcarbide by the pH and concentration of potassium permanganate.

A 4H semi-insulating single crystal silicon carbide wafer was polishedwith 6 different polishing compositions. Each of the polishingcompositions contained 0.6 wt. % titania and potassium permanganate. ThepH and the amount of potassium permanganate are indicated below in Table15.

The silicon carbide removal rate (nm/hr) was determined for eachpolishing composition, and the results are shown in Table 15.

TABLE 15 Potassium Permangante Polishing Concentration Silicon CarbideComposition (wt. %) pH Removal Rate (nm/hr) 15A (invention) 0.05 2 48515B (invention) 0.45 2 1236 15C (invention) 0.05 4 289 15D (invention)0.14 4 389 15E (invention) 0.05 6 69 15F (invention) 0.45 6 129

As is apparent from the data presented in Table 15, use of titania overa pH of 2 to 6 at a variety of potassium permanganate concentrationsresulted in a significant silicon carbide removal rate.

EXAMPLE 16

This example demonstrates the effect on the removal rate of 4HN singlecrystal silicon carbide by a polishing composition.

4HN single crystal silicon carbide wafers were polished with threepolishing composition containing seeded gel process alpha alumina andeither potassium permanganate, potassium persulfate, or periodic acid,adjusted to a pH of 4. The amount of abrasive and the amount ofoxidizing agent are indicated in Table 16.

The silicon carbide removal rate (nm/hr) was determined for eachpolishing composition, and the results are shown in Table 16.

TABLE 16 Oxidizer Alumina Silicon Carbide Polishing ConcentrationConcentration Removal Rate Composition (wt. %) (wt. %) (nm/hr) 16A(invention) 0.3 wt. % potassium 0.6 341 persulfate 16B (invention) 0.4wt. % potassium 0.6 2055 permanganate 16C (invention) 0.2 wt % periodic0.2 698 acid

As is apparent from the data presented in Table 16, the inventivepolishing compositions were able to successfully polish 4HN singlecrystal silicon carbide wafers.

EXAMPLE 17

This example demonstrates the stability of potassium permanganate in anaccelerated heating test to simulate the decomposition of oxidizingagents at room temperature.

The silicon carbide removal rate, pH, conductivity, and % oxidizer of apolishing composition containing potassium persulfate and a polishingcomposition containing potassium permanganate were measured initiallyand after heating to 62° C. for 16 hours. The results are shown in Table17.

TABLE 17 Potassium Potassium Potassium Potassium Persulfate Persulfate(16 Permanganate Permanganate (16 Oxidizing Agent (initial) hours at 62°C.) (initial) hours at 62° C.) Removal rate 251 164 1148 1139 (nm/hr) pH3.75 1.90 3.84 3.88 Conductivity 5520 11,350 1198 1185 (μS/cm) %oxidizider 0.598 0.297 0.170 0.170

As is apparent from the data presented in Table 17, potassiumpermanganate does not decompose but rather remains stable under theaccelerated heating test.

All references, including publications, patent applications, andpatents, cited herein are hereby incorporated by reference to the sameextent as if each reference were individually and specifically indicatedto be incorporated by reference and were set forth in its entiretyherein.

The use of the terms “a” and “an” and “the” and similar referents in thecontext of describing the invention (especially in the context of thefollowing claims) are to be construed to cover both the singular and theplural, unless otherwise indicated herein or clearly contradicted bycontext. The terms “comprising,” “having,” “including,” and “containing”are to be construed as open-ended terms (i.e., meaning “including, butnot limited to,”) unless otherwise noted. Recitation of ranges of valuesherein are merely intended to serve as a shorthand method of referringindividually to each separate value falling within the range, unlessotherwise indicated herein, and each separate value is incorporated intothe specification as if it were individually recited herein. All methodsdescribed herein can be performed in any suitable order unless otherwiseindicated herein or otherwise clearly contradicted by context. The useof any and all examples, or exemplary language (e.g., “such as”)provided herein, is intended merely to better illuminate the inventionand does not pose a limitation on the scope of the invention unlessotherwise claimed. No language in the specification should be construedas indicating any non-claimed element as essential to the practice ofthe invention.

Preferred embodiments of this invention are described herein, includingthe best mode known to the inventors for carrying out the invention.Variations of those preferred embodiments may become apparent to thoseof ordinary skill in the art upon reading the foregoing description. Theinventors expect skilled artisans to employ such variations asappropriate, and the inventors intend for the invention to be practicedotherwise than as specifically described herein. Accordingly, thisinvention includes all modifications and equivalents of the subjectmatter recited in the claims appended hereto as permitted by applicablelaw. Moreover, any combination of the above-described elements in allpossible variations thereof is encompassed by the invention unlessotherwise indicated herein or otherwise clearly contradicted by context.

1. A method of chemically-mechanically polishing a substrate, whichmethod comprises: (i) contacting a substrate comprising at least onelayer of single crystal silicon carbide with a chemical-mechanicalpolishing composition comprising: (a) a liquid carrier, (b) an abrasivesuspended in the liquid carrier, wherein the abrasive is alumina and ispresent in an amount of about 3 wt. % or less based on the weight of theliquid carrier and any components dissolved or suspended therein, and(c) an oxidizing agent, wherein the oxidizing agent is present in anamount of about 0.001 wt. % to about 2.5 wt. % based on the weight ofthe liquid carrier and any components dissolved or suspended therein,and wherein the oxidizing agent is selected from the group consisting ofhydrogen peroxide, oxone, ammonium cerium nitrate, periodates, periodicacid, iodates, persulfates, chromates, chlorates, permanganates,bromates, perbromates, ferrates, perrhenates, perruthenates, andmixtures thereof, and (ii) moving the polishing composition relative tothe substrate, and (iii) abrading at least a portion of the siliconcarbide of the substrate to polish the substrate.
 2. The method of claim1, wherein the abrasive is present in an amount about 1 wt. % or lessbased on the weight of the liquid carrier and any components dissolvedor suspended therein.
 3. The method of claim 1, wherein the oxidizingagent is present in an amount of about 0.1 wt. % to about 0.5 wt. %based on the weight of the liquid carrier and any components dissolvedor suspended therein.
 4. The method of claim 1, wherein the liquidcarrier with any components dissolved or suspended therein has a pH ofabout 2 to about
 6. 5. The method of claim 1, wherein the oxidizingagent is potassium permanganate.
 6. The method of claim 1, wherein theoxidizing agent is periodic acid.
 7. The method of claim 1, wherein thesilicon carbide is removed from the substrate at a rate of about 30nm/hr to about 2700 nm/hr.
 8. A method of chemically-mechanicallypolishing a substrate, which method comprises: (i) contacting asubstrate comprising at least one layer of single crystal siliconcarbide with a chemical-mechanical polishing composition comprising: (a)a liquid carrier, (b) an abrasive suspended in the liquid carrier,wherein the abrasive is selected from the group consisting of alumina,titania, ceria, and zirconia, and wherein the abrasive is present in anamount of about 3 wt. % or less based on the weight of the liquidcarrier and any components dissolved or suspended therein, and (c) apermanganate salt, wherein the permanganate salt is present in an amountof about 0.001 wt. % to about 2.5 wt. % based on the weight of theliquid carrier and any components dissolved or suspended therein, (ii)moving the polishing composition relative to the substrate, and (iii)abrading at least a portion of the silicon carbide of the substrate topolish the substrate.
 9. The method of claim 8, wherein the abrasive ispresent in amount of about 1 wt. % or less based on the weight of theliquid carrier and any components dissolved or suspended therein. 10.The method of claim 8, wherein the abrasive is alumina.
 11. The methodof claim 8, wherein the permanganate salt is present in an amount ofamount of about 0.1 wt. % to about 1 wt. % based on the weight of theliquid carrier and any components dissolved or suspended therein. 12.The method of claim 8, wherein the liquid carrier with any componentsdissolved or suspended therein has a pH of about 2 to about
 6. 13. Amethod of chemically-mechanically polishing a substrate, which methodcomprises: (i) contacting a substrate comprising at least one layer ofsingle crystal silicon carbide with a chemical-mechanical polishingcomposition comprising: (a) a liquid carrier, (b) an abrasive suspendedin the liquid carrier, wherein the abrasive is selected from the groupconsisting of alumina, titania, ceria, and zirconia, and wherein theabrasive is present in an amount of about 3 wt. % or less based on theweight of the liquid carrier and any components dissolved or suspendedtherein, and (c) periodic acid or periodates, wherein the periodic acidor periodates are present in an amount of about 0.001 wt. % to about 1wt. % based on the weight of the liquid carrier and any componentsdissolved or suspended therein, (ii) moving the polishing compositionrelative to the substrate, and (iv) abrading at least a portion of thesilicon carbide of the substrate to polish the substrate.
 14. The methodof claim 13, wherein the abrasive is present in amount of about 1 wt. %or less based on the weight of the liquid carrier and any componentsdissolved or suspended therein.
 15. The method of claim 13, wherein theabrasive is alumina.
 16. The method of claim 13, wherein thepermanganate salt is present in an amount of amount of about 0.1 wt. %to about 0.5 wt. % based on the weight of the liquid carrier and anycomponents dissolved or suspended therein.
 17. The method of claim 13,wherein the liquid carrier with any components dissolved or suspendedtherein has a pH of about 2 to about 6.